In recent years, progress has been made in the research and development of organic EL elements that use the phenomenon of electroluminescence occurring in solid fluorescent materials. Being self-light-emissive, the organic EL elements have characteristics such as a fast response speed, a wide viewing angle, a high contrast and the like. Each organic EL element includes a lamination of a pair of an anode and a cathode, and an organic light-emitting layer therebetween. The organic light-emitting layer causes the phenomenon of electroluminescence to occur by recombination of carriers (holes and electrons).
As a method for forming a film of the organic light-emitting layer, there is known a solution-deposition-type film forming method (see, for example, Patent Literature 1). The solution-deposition-type film forming method is considered to be preferable from the point of view of the mass production. In the solution-deposition-type film forming method, an organic light-emitting layer material, which contains a solvent and a material constituting the organic light-emitting layer, is applied onto the substrate by the ink jet method (liquid droplet ejection method) or the like, and the organic light-emitting layer is formed by drying the applied organic light-emitting layer material by using a vacuum apparatus (see, for example, Patent Literature 2). The vacuum apparatus used in this procedure is mainly a vacuum apparatus that has a vacuum chamber and a vacuum pump. For drying the organic light-emitting layer material, a substrate with an applied film of the organic light-emitting layer material formed thereon is placed in the vacuum chamber whose internal pressure has been reduced by the vacuum pump. The vacuum apparatus is also used to house the organic light-emitting layer that has been formed by the drying, until the next procedure is performed.
In general, a lubricant, a vacuum sealing material and the like are used in a portion of the vacuum pump that is connected to the inside of the vacuum chamber. Furthermore, the lubricant, the vacuum sealing material and the like contain an antioxidant for preventing the materials constituting the lubricant, the vacuum sealing material and the like from oxidizing.